Automatic operator



Aug. 11, 1936. s. L.\KERR 213505333 AUTOMATIC OPERATOR Filed Nov 20, 1929 8 Sheets-Sheet 1 4/ INV NTH'OR Aug. 11, 1936. s KER V I 2,0503% AUTOMATIC OPERATOR I Filed Nov. 20, 1929 8 Sheets-Sheet 2 'm /r/m' mam 12 a/v/r/ms S. L. KERR AUTOMATIC OPERATOR Filed Nov. 20, 1929 &

KI I I I I 8 Sheets-Sheet 3 vAug- 1936. s. L. KERR AUTOMATIC DPERATOR Filed Nov 20, 1929 B'Sheets-Sheet 4 I m i I a Aug. 11, 1936. KERR 2,050,338

AUTOMATIC OPERATOR Filed Nev. 20, 1929 a sheets-sheets 12 7.9. .fiyja Aug. 11, 1936. I 5 KERR 2,050,338

Au'rol'wnc OPERAVTOR I Filed Nov. 20, 1929 8 Sheets-Sheet s I rum/rm Aug. 11; 1936. vs. L KERR 3 AUTOIAT I G OPERATOR rna i Nov. 20, 1929 a Sheets-Sheet s. KERR 2,050,338

AUTOMATIC OPERATOR Filed Nov. 20, '1929 Aug. 11, 1936.

l lmllllk 8 Sheets-Sheet a means... 1'1

NITED STATES.

P TE ToF icE r amass I .w'rom'rrc ornaa'roa Samuel Logan Kerr, mus ums, Pa.

I Application November 20. me, Serial No. 408,544

sacrum (01.280-4) tration, in connection with a hydro-electric gen-g crating station. I

The processes involved in the operation of such a station have heretofore been accomplished primarily by manual means using one or more operators on constant duty. The operator's function is to start and stop units, place them in parallel with the generating system and adjust the total output to meet the demands of the power users or to correct the system speed or frequency to nominal, and also to adjust the load between units to secure the most economic distribution of loads or to adjust the output of the station in combination with other stations to secure the most economic combination.

The variations in requirements for each of these functions, particularly those dealing with a change in demand or a change in speed. occur rapidly and at frequent intervals thus necessitating constant manual attention of the personnel to maintain a commercial standard of operation. However, to secure a higher standard oi operation requires closer attention on the part of the operating personnel than is reasonable to demand from them, or than is practically possible to secure.

For a better understanding of my invention a brief description will begiven of the usual duties of the operators in such a station. In this example which may be modified to apply to any number of specific installations, it is assumed that there are several units in the station, for

example, three, and that this station supplies power directly to the various power users and that no additional generating units are in parallel with this system.

with several units in service delivering power to the-distributing system described above, the

station output will be fixed by the demands of the various power users, and the individual unit governors will act to correct appreciable changes in speed caused by the differences between the supply and demand. with the regular character? istlcs of alternating current generating units a drooping characteristic of speed with respect to output is necessary for the purposes of obtaining stability with the usual type of speed governor. Thus if the plant is operating at normal speed, and the demand increases, the final speed attained with a stable condition would be a somewhat small percentage below normal. The op- 5 erators function then is to increase the load on the generating units by adjusting the remote control switches on .the load adjusting motors of the unit speed governor in such a manner as to increase the output a sufiicient amount to bring the speedback tonormal and thus maintain the normal speed of the system at a constant value.

After the speed has thus been adjusted to normal ii the demand'should thendecrease the speed will go above normal. In this case the operator would manipulate the switches on the load adjusting motors of the governors so as to decrease the output slightly and thereby return the speed to normal. The general functions described above may be termed the correction of by manual means.

In the case'where more than one unit is in service the operation becomes more complicated since if the operator adjusts the load on only one unit the other units will change their load automatically due to being returned to their normal speed through the parallel or synchronized connectionwith the adjusted unit. However, the load distribution between units obtained in this manner will'not necessarily be in accordance with the requirements for the best operating efflciency. .It is a well established fact that there is a certain definite schedule for the loading of the various units to secure the best combined economy.. The function of the operator in addition to correcting the speed to normal is also to redistribute loads between the various units in the plant in accordance with the predetermined schedule for economy. since each unit may have ditlerent characteristics from the other units in the station the schedule may call for unequal distribution of load between units; In the case where all the units are alike in a station, the schedule may .call for them to divide the load equally under all conditions or an unequal distribution of load may be effected within certain ranges tosecure the best results.

In any case a fixed schedule must be maintained-to securethe. maximum efilciency of the combination. The operator therefore is under for him tomanipulate the switches on the load irequency to' normal 20 adj" rtingmotors of the various units in the usual manner, namely to raise or lower the station output to correct the frequency and then to readjust the load between units to maintain the schedule for economic loading and at. the same time not disturb the system frequency from normal. i As the variations in demand increase the requirement on the part of the operator to maintain constant speed is still further increasedand for most all plants the continuous attention of the operator is required in order to even appreach the fulfillment of constant frequency and economic load distribution between units.

In the case where the generating system would consist of more than one plant the same general procedure would be followed, except that each plant would be assisting in the correction of system speed while the combined load sched-' ule for the distribution of output between plants could be maintained in the same way as the schedule for load distribution between units with the same object in view, namely, that of securing the most efficient operation of the combina-* tion. In the case of severalplants there is of course theindividual loading schedule for the various units in each plant in addition to the schedule for the station as a whole with respect to the other plants on the system.

The case where the' units in a given plant do not have the same characteristic of efliciency with respect to output becomes-more complicated since it requires unequal distribution of load between units. A definite schedule can be worked out based on the individual unit characteristics so that for .any output of the plant the distribution of load between the various units will be for maximum economy. In such a case where, for

In my invention the functions of the operator are performed by automatic equipment which will maintain the economic distribution of load between the various units or combination of units in any plant or group of plants, simultaneously with the correction of the frequency to normal following variations in demand or will maintain a fixed output on a given station simultaneously with the economic distribution of load between the units in service. One object of my'control equipment is to reduce the losses resulting from incorrect load distribution to a minimum, and hence increase the emciency of operation of any plant or group of plants by maintaining the ideal schedules for loading distribution or for other operating functions of the station.

These functions are accomplished automatically in my invention by the provision of a combination of instruments and circuits which indicate the output of each unit or the gate opening of each individual unit, or some function of the unit whichis proportional to the output, or the discharge. If the relation of the outputs or these other functions is established from the unit characteristics then the control equipment is. applied insuchamannerthatitwillbesensitivetoa' variation from the ideal schedule which in turn will cause contacts to be closed to operate the load adjusting devices of the prime mover in such a manner as to correct for the difference existing.

In a group of units it is possible to determine the correct relation ofoutput with respect to each other and the combination of elements in my control equipment is such that it will maintain this relation through the actuation of the load adjusting devices on the prime mover. To effect in addition a correction for frequency, some form of frequency sensitive apparatus is employed which will operate contacts whenthe frequency varies above or below the desired value. By making these contacts, electrical control impulses cause the loadadjusting devices on the individual unit governors to be moved to increase or decrease the output in accordance with the departure of the frequency from normal. These control impulses may be arranged to effect the output of one or more units while intermediate or simultaneous contact may be provided for the load distributing functions of the control. In cases where the station output is to be main-, tained constant some form of indication of the total station output or some other variable which is in a known relation to the station output may be used asa base for the control. Some instrument sensitive to this variable is used in my combination to actuate contacts if the station output departs from the desired amount. These contacts act to change the setting of the load adjusting mechanism on the governor in such 'a manner as to restore the station output to the desired amount. Simultaneous or in coordination with these impulses are the secondary impulses for load distribution between units, and thus the station output is maintained at a constant value and the individual unit loadings are maintained at their desired schedule for maximum eiliciency. V

This same general plan is used in connection with the supplying of a fixed amount of power to any given customer of the power company by connecting, for example, a watt-meter in the supply line to the particular customer and having the contacts arranged sothat they act to incontacts act to reduce the output on the units through the load adjusting devices, or vice versa crease or decrease the station load in such a manif the supply to the customer falls below the desired amount. In this manner the automatic equipment performs the functions of the ideal operatorin being constantly alert to variations in frequency in output along with other functions which it is desired to control. e

In one specific, embodiment of the invention as applied to a hydro-electric station of say three units, two units of which are alikeand one unit different from these two, the arrangement of the control equipment is as follows: Each unit is equipped with a watt-meter having a shaft which moves in direct proportion to the unit output and which is used to drive a disk having what is called a load transmitting variable resistance placed around its circumference. Another variable resistance called a load setting resistance is a dupii cate of the first, but is manually adjustable.- These two resistances are connected electrically in parallel and constant potential maintained on theirterminals. Bridged across these resistances is a galvanometer circuit, connectedwith' each resistance through suitablecon tacts which 5 permit each resistance to be moved relative to its respective contact. Thus with the manually adiustable resistance set in any given position there willbe a corresponding position on the other resistance at which the potential will be thesame m on each resistance contact of the bridged gal-. vanometer circuit and hence the galvanometer' will be in neutral position. as the output of the unit varies. the watt-meter operated resistance .is-

:5 tential. Proper scales are employed which are calibrated in terms of the unit output so that the manuallyoperated dial is set'to a given output and the bridge circuit will be balanced when the watt-meter driven potential is equal to this .0 .value and, hence the unit output equals the manually set amount. The variable contact-making device is controlled by the galvanometer so that, upon a load variation, an electrical circuit connected to the load adjusting motor is inter- 5 mittently closed whereby the load adjusting motor is energized by impulses. These control impulses cause the load adjusting device on the governor to increase or decrease the unit output in accordance with the potential controlled v L by the watt-meter.

The above case takes care of the maintaining of a fixed load, on any one unit. When a combination of units are employed, for example units having the'same characteristic, the manually ad- .justable resistance described above can be connected to both units, through an individual contact-making galvanometer and control circuit on each unit, in such a manner that both units will carry a load-corresponding to the setting on a ,0 single master load-setting dial. In the case where a unit having dissimilar characteristics is operated in combination withthese two similar units then two sets of manually adjustable resistances are employed one of which is connected to the 5 units having similar characteristics and one of which is arranged in combination with the controls of the dissimilar unit. This arrangement is constructed in such a manner that two COlltact points, one for each resistance, have 'po-' D tentials in proportion to the desired fixed output of the respective units, this proportion being in accordance with the ideal loading schedule. Each contact is connected to the bridge circuits of the proper individual units so asto adjust the 5 loads on the units in the proper proportion; In this manner proper schedule of the load on each unit is maintained since the two potentials on the manually set resistance are in proportion to this desired output on each unit, and the individual unit galvanometer will not be balanced until the.individual unit watt-meters transmit a potential equal to that on the manually set resistance and hence each unit has a correct amount of output. v c i In a case where the station is to control fregmosasssfs i quency some of frequency sensitivejeviee is I employed as in combination with a contactvmu device which will contacts when the ire 'quency departs from normal. These contacts in turn are connected tothe samerelays which are 5- used in connection with the fixed local control just mentioned "but arrangements are made so that the control impulses from the frequency sensitive device will be transmitted to one unit and the variation in output oh this unit determines the 10 output of the remaining unitsby the amount 01' potential transmitted from the watt-meter driven resistance against the potential or the watt-meter driven resistances of the otherunlts. In this way the individual unit galvanometer on unitscther 1i than the unit'receiving the impulses for frequency 1 control willbe deflected if the Output on these individual units differs from the potential which is transmitted irom the frequency control. Hence the distribution r load .between the units is a as function of the variable potential whichis trans: mitted as a function. of the output of theirequency controlling unit. By the proper displace I ment of resistance around this disc, driven from the watt-meter it is possible to transmit any del sired potential either as a direct or variable tune tion of the output of the frequency controlling unit in such a manner that the other unit bridge circuits will be balanced at some variable output oi the individual units with respectto the ;i.'re- N quency controlling unit and thus maintaining the economy schedule of. load even though the whole station output is varied due to the requirements for frequency correction. Frequency cone trol impulses can also be given to all units simulill taneouslyandthe watt-meter resistances. on each individual unit arranged with the unit bridge circults so that intermediate equalizing impulses are given to the units in such a manner that the schedule for economic load is maintained. 40

Other objects and advantages of my improved I arrangement willbe seen from the following description of the accompanying drawings in which:

Figs. 1 and 1a together comprise a detailed disclosure of the instruments and their wiring con- 5 1 nections, although for simplicity and clarity the frequency selector switch is shown as a ity of independent knife switches. Fig. 2 is a fragmentary detail showinga battery. or other sourceof current in place of certain other transformers.

Fig. Sis an isolated and simplified wiring diagram "of the galvanometer circuit bridged across the parallel connected unit load setting and transmitting resistances,

Fig. 4 is a diagrammatic perspective of the contact making device in position for making a series oi successive contacts, a

Fig. 5 is a perspective of a contact making device in position whereby no contacts will be made, so

Fig. 6 is an elevation 01' one form of interrupter. c i I Fig.7 is another form of interrupter that may be "used,

, Fig.18 is an enlarged viewoi' one portionoi' the 76 totaliaing watt-meter andload limit equipment with a further element attached thereto for autochanical means for distributing the load in accordance with the unit characteristics.

In considering the specific application of my invention to hydraulic plants it will of course be blue in the accepted manner.

understood that the usual hydraulic equipment remains unchanged. The speed governorat all times functions in its normal manner to control fluid distribution to the gate operating servo motors thereby to control the power of the turmechanism may be employed between the speed governor and turbine gates while any of the other control devices such as overspeed governors, safety appliances'or the like may also be used.

Usual restoring If the prime mover is of the steam turbine or I internal combustion'engine type the type of governor and power control valve mechanism usually employed therewith may beused and these will operate in their usual manner with thefunctions T of my improved arrangement simply superimposed on the functions thereof as in the case of the hydraulic governor.

Unit load setter and transmitter: wattmeter:

constant load on single unit.--A watt-meter l0.

Fig. 1a is connected in any usual manner to indicate the output of its unit No. l.

pointer movable along a rotatable screw-threaded shaft which is arranged to drive mechanically, through suitable means such as a' belt or chain il,"a load transmitting variable resistance I! of a unit load transmitter and setter generally indicated at I, This device'operates only in accordance with the'load on its particular power unit.

The resistance I2 is diagrammatically shown as being rotatably actuated through a worm and worm gear although the actual device may employ various of mechanical arrangements depending somewhat upon the type' of watt-meter and resistance used. 1 Y

The load transmitting resistance is connected electrically in parallel with a load setting resist- This watt-' meter may be of any suitable type although, for .purposes of illustration, there is shown diagrammatically a usual' type having its indicating ance I! which is manually adjustable by a suit able handwheel. A potential, maintained across two ends of the parallel connection, is trans-- mitted from a standard potential transformer i4,

which is energized by current from main buses, through wire Ii, terminal wires l6, l1, resistances l2 and I3, terminal wires-l8, l8 and back to transformer it through wire 20. A battery circuit I), Fig. 2, having an adjustable resistance Il may, if desired, be used for the source of potential instead of transformer I4 and the corresponding transformers for the other units.

Bridged across the resistances, is a galvanometer circuit comprising a terminal II, wire 22,

galvanometer 23, wire 24, manually adjustablev resistance 26, wire 21, switch II set in position II, wire Ill and terminal ll of resistance II. The

parallelresistance and bridge galvanometer circuits are shown diagrammatically in the isolated view Fig. 3. v i

tact-making device) .In the controller generals,'oso,sss

It will be seen that-for a given position of contact 3| on unit load setting resistance II there is a corresponding position for contact II on resistance It at which no potential diiference will exist between contacts II and II and-therefore no currentflow in the galvanometer circuit. Also, the direction of current flow through this circuit depends upon which direction resistance l2 moves from said corresponding point; This movement is effected by changes in load as inis dicated by the watt-meter and hence an increase or decrease in load on the unit will cause current to flow in one or the other 'of opposite directions-through the galvanometer circuit. This feature is used to determine any fixed load at which it is desired tomaintain the unit. Load variations, either up or down, from this fixed value will be only temporary as the mechanism responsive to the direction of current flow in the r galvanometer will act to correct these variations and bring the load back to the given desired value as fixed by the position of point II with respect to resistance It. Load controller (galvanometer controlled conly indicated at 35 and to be described now, I use a well-known instrument in a novel manner so as to perform certain new functions with my coni- I bination. This mechanism comprises a contactmaking device generally indicated at 18, see Figs.

4 and 5, arranged so that when the galvanometer circuit has no current flowing therethrough the zero or balanced position of the galvanometer pointer 3! lies directly under a gap between adjacent ends of levers 38 and I9, Fig. 5. A cam 40 on a cam-shaft 4i, continuously driven by a motor 42, Fig. 1a, through any suitable means diagrammatically shown as a belt and pulley l3, raises a'rocker arm 44,- Fig. 4 pivoted at II. This rockerarm in lifting picks up the galvanom- 0- .arm 50, Another pin 52 cooperates'with arm it when the galvanometer pointer is swung in the other direction by current flowing in the opposite direction-in the galvanometer circuit.

when rocker arm ll rises, a cam 83 simulta- 55 neously moves arm 54, and its pivotally carried cross arm ill, outwardly away from. disk I. On the next half revolution of cam shaft ll, cam I! permits arm "to move back toward disk BI. likewise carrying cross arm 50 which in its tilted position frictionally engages disk 55. By the time this frictional engagement is effected, shaft II has rotated cams I1 and BI so'that one or the other engages fingers it or ill to move cross arm to back to its horizontal position, Cams 53 and Ill rotate together so that rocker arm 44 releases its hold on galvanometer pointer 11 after the frictional contact has been made, thereafter permitting arm 41 to be returned to its neutral position by pin it attached to cross arm II when the cross arm is being returned to its horizontal position by cam' 51. The above cycle of operations is repeated if, on the next revolution of the I continuously rotating cam shaftli, current is 7 still flowing to the galvanometer circuit so as to I deflect the pointer. Ii thegalvanometer currentflows .in the opposite direction cross arm' 69 is oppositely deflected by the short leg 39 lever 46 through pin 62. Cross 69 isthen returned to its horizontal position by cam 69 contacting finger 99. From'the above .it is seen that depending upon the'direction of current flow in the gaivanometer circuit one or the other ot cams and fingers 91, 69 or 69, 69will have intermittent contact with each other until the galvanometer current is reduced to zero. Also, as the galvanometer pointer gradually moves toward its neutral point, due to diminishing current, the length of time of contact between either cam and its cooperating finger becomes correspondingly shorter. This is because the amount that arm 99 is rotated depends upon the magnitude oi the galvanometer deflection for as the deflection decreases the pointer moves away i'rom the fulcrum oi the levers 46 and 41 and toward the gap be-' tween the short legs 49.

In my invention, I utilize this intermittent 0011- I tacting by Providing stationary brushes 62 and 69 slidably engaging and having electrical contact with cams 61 and 58 which are suitably insulated from, but fixed to, cam shaft 4| while a common or neutralcontact 64 is diagrammatically shown engaging the disk and through the contact 0! cross arm 69 with the disk completes the circuit between 63 and 64 by means of cams 69 and 69 or between contacts 62 and 64 by means of cam 61 and finger 69. v Load adjusting motor operated by load control circuits-The load adjusting motor of the speed governor controlled by the above mechanism is as inflows: With a desired value of load as set by dial 9 indicating the position of resistance II, it

watt-meter l9 responds to a change in load, then loadftransmitting variable resistance I2 is rotated and a potential difference in the galvanometer circuit results between points 2| and 3| as described, thereby deflecting the galvanometer pointer 91, Fig. 1a. Contacts 69 or 69 are thereupon closed depending upon whether the load variation is an increase or decrease with respect to the desired fixed value set by dial 9.

In making these contacts the load adjusting motor 69 on the unit governor, diagrammatically represented at 91, is rotated in the proper direction for increasing or decreasing the load on the unit depending upon which of contacts 99 or 99 is closed by the galvanometer. The mechanism controlled by this motor for adjusting the turbine gates or control valve is well known and need not be described here. 2

In order to make or break currents oi sufllcient size to actuate the load adjusting motor 66, it is necessary to use relays of high resistanceactuated by the resulting small current whichis preferably used on the contact-making device 99. This current is supplied through a common wire 64, Fig. in, from a source which will be later described. When finger I9 and cam 99 make contact, current fiows from common wire 94, through brush contact 99, wire 69, switch 19 set in up position, wire vl2, actuating coil on relay I9, wire 14, contacts 16 of manually operable switch I1 and wire 19 to the other side 01' the source, oi said current supply to be described later, thereby energizing and closing relay I9. v Current then passes from wire 19 connected to the source," through adjustable resistance 16, wire 19, 99 and 9| to energize lowering field li of the split field load adjusting motor 66, and to the opposite side or a direct current sup- 69, and to the other side of the current source as described for relay 13, thereby energizing and closing relay 99 to permit current flow from wire, through wires 9i and 92 to energize the raising. field 93 of load adjusting motor 66.

Manual control of load adjusting. motor.If it is desired to disconnect the automatic operation of load adjusting motor 66and operate same manually while at thesame time eliminating anypossibility of the two controls being accidentally or intentionally placed in operation simultaneously, thereby possibly burning out the motor, the manuallyoperable switch 11, shown for pur- 29 poses of illustration as a push and pull switch, is moved to close either contacts 95 or 96 by contactor 91. In either position contacts 16 will be opened to disconnect the automatic control of the load adjusting motor, whereby the motor is placed 25 solely under manual control.

When contacts 95 are closed current is supplied from source 95 through wires 99 and 99 to lowertrol impulses are transmitted to the units fol- 4 lowed by an interval with no control impulses. This allows the governor and load adjusting device to reach a position of stability and eliminates the difiiculty which would be experienced 45 due to .over-shooting oi the control mechanism caused by too many contacts being made by the contacting cams and fingers oi the galvanometer control and too many impulses thereby being transmitted to the load adjusting motors without permitting sufiicient time for the unit and its governing mechanism to reach a'position of stability. The action of this interrupter mechanism will be seen to have an efiect on the control systemsimilar to the restoring mechanismon the governor, as it introduces a stabilizing element in the control equipment.

The interrupter H9 is placed in a neutral lead Ill, connected to 'wire ll! of the negative --side of the direct current supply 96. in such a manner that the current supply to the reiaydevices and other control equipment connected to neutral lead Ill, may beinterrupted. This neutral lead is connectedthrough switch I99, on unit No. I, and wire H9 to. the common contact 64 of the galvanometer contactmaking device 96. The interrupter device consists oi a small motor I I4 continuouslydrivi'ng a drum M5, on which is located a continuous slip ring I I6 connected at all times tocontact I I1 01' neutral line III, which also has an adjustable contact H9. Additional strips on this rotating drum in the form of su'ccessively shorter segments are shown at 9, 129 and Ill each being electrically connected to the Closure of contacts 96 connects 30.,

either continuously or intermittently to galvanometer contacting device 28 thereby obtaining the results previously described.

An alternative form of the interrupting device,

-Fig. 6, can be arranged with a tapered strip of metal I22 formed on the'periphery of the drum;

The portion I23 corresponds to slip ring 4 while contact I II is adjustable along the cylinder by means of the hand wheel and screw I24 so that a fine control can be secured in the ratio of the time of contact to the time that current is.

cut off. This tapered strip could-be made as a projection from the face of the drum so as. to close a pair of contacts mechanically.

The result can also be secured as shown in Fig.

'7 by means of a series of continuously rotating -cams I25, I25a and I251), arranged on a shaft which closes sets of contacts I26, I26a and I26b and completes the neutral circuit III depending upon which one of the switches I21, I2Ia and .l2lb are closed. The cam surfaces of eachcam are different so that the length of time of contact is varied in a similar manner to that effected by segments l I 9, I2II and I2I of interrupter drum H5. The effect of continuous contact H8 is secured by short circuit switch I28.

Master load setter.1n the arrangement whereby the unit is controlled from a master load setter I40 the.manually adjustable resistance I3 is disconnected from the circuit previously described for individual unit control and the master load setter pla'ced in operation by throwing switch 28 from position 29 to I. d

The master load setter I40 has a manually adjustable resistance I42 which is substituted for unit load setting resistance I3 in the parallel circuit containingresistance I2. While resistance I2 is still supplied with current from transformers I4 by wires I5 and 20, resistance I42 is supplied through wires I44, I45 and I48 from a transformer I43, which is a-duplicate of I4.

A contact I41 in the master setter corresponds to contact II in the replaced resistance l3. Contact I41 transmits any potential through wire I48, switch A-2 in position 1, connecting with wire 360, switch AI, also in position I, wires ISI and I52, switch 2! closed in position III, wires 21 and 24 through galvanometers 22 and wire 22' to contact 2| of resistance I2. Thus the galvanometer is bridged across a parallel ar-' rangement oi the unit load transmitting resistance I2 and master load setter resistance I42 in the same manner as when the unit load setter and transmitter resistances were connected in parallel with each other. Master load setter resistance I42 and unit load transmitting resistance 12 are connected by common wires I94 and I 99 through switch III! to insure the same potential on-each resistance. 7

The control of output is accomplished in the same manner as with the individual load control on the-unit'wh'en' using dial 8 and its manually 1 variable resistance I2. with the load set from -116 the master load setter I40, by use of a suitably a,ooo',ssa s '4 l tactIIl canbemovedirom itssliprlngposition 141 in the same manner as with unit-No. I.

-without master control.-If two units have disgraduateddiai IN anditsreslstanoe I42,thegalvanometer 22 moves in proportion to the diilerence in potehtiai existing between contacts I41 o and 2i. The contact-making device '34 closes either contact finger ll or ll,'with its correspond- 5.

ing relay II or II respectlvelyydepending upon a whether the potential at contact 2| is above or below the potential existing at contact I". I

Interconnected operation contml by master load setter of duplicate units to give fixed combined load.with units Nos. l and I beins dupli- 'cates in so far as having substantially identical operating characteristics. the control equipment and its operation for unit No. I will be identical with that described for unit No. I. For simplicity 15 v elements in units 1 and 3 will be referred to with the same reference number but with the suflix letter a indicating unit No. I. The description of unit operation of unit No. I will-sufllce for the unit operation of unit No. 2. However, where 20 units I and I are both controlled from the master load setter I40, switch IIISa is closed to energize the potential circuit from transformer I42'a while switch 24a is placed in position I4Ia whereby unit load setting resistance Ila is disconnected from 25 its parallel relation with unit load transmitter resistance I2a and-the latter placed in parallel with master load setter resistance I42. The parallel connection is present because each of the resistances are connected to a common source of current through the respective transformers I43,

I4 and Ila and wire I98 which commonly connects the resistances. The galvanometer 22a is bridged across master load setter resistance I42 and unit load transmitter resistance I2a from 35 contact 2Ia,' wire 22a, galvanometer 23a, switch 28a through wire Ina which connects to wire' I52 and thence through switch A-I to contact This circuit when isolated and simplified is shown in Fig. 8. Hence galvanometer 22a will move in response to a difference of potential between points I41 and 2Ia in exactly the same manner as galvanometer 22 moved in proportion to the dinerence in potential between points I41 and 2| and will thereby operate the load adjusting motors 4i and a to give and maintain the proper load division between units l and 2. Thus in this interconnected operation, the single manually ad- Justable master resistance I42 by a proper load 50 setting on dial I53 will determine the stable posiwhich has been calibrated in conjunction with the master load setting resistance I42 and the unit load transmitting resistances I2 and I21: and their dials I and la.

Load control of dissimilar unit operating alone similar characteristics so that, for example, best efllciency occurs at diflerent loads on each unit,

the two unitsshould be so controlled as to operate simultaneously at different loads. To accomplish this when either or both of similar units I and I are in service at'the same time that it is desired to operate unit 2, which is dissimilar to the other units, independent control equipment such as described with the other units 'is provided for unit 2 except that the manually ad- 10 justable unit load setting resistance lib may diiier from itscorresponding resistances I2 and "a by not being uniform in resistance in proper--- tion to its angular displacement in which case dial 917 is calibrated accordingly. 7

The unit load transmitting resistance I2b may also diifer from its corresponding resistances I2 and I 2a in not being uniform; with these resistances due to specialrequirements for other types of operation hereinafterdescribed. As long as these special requirements are not present the resistance may be considered uniform.

A switch, generally indicated Illb, diflers from its corresponding switches III! and "Na by comprising two two-pole switches IDBb and lbs' b also for special requirements. -When switch IIIBb alone is referred to as being closed or opened it includes both switches. Otherwise the control equipment is the same as in the other units so that reference to corresponding elements in the units is by the same reference numbers except the suflix letter b indicates the elements in dissimilar unit No.2, while suflix letter a as seen, denotes unit No. I. a

When unit'No. 2 is operating alone switch 28b is in position 29b.C The control operation is then the same as in theother units when operating alone. so that the previous description therefor will suillce here. I

Dissimilar unit operating alone with master controL-T control unit 2 from the master load 24b, through galvanometer 23b and wire 22!) to contact Ho. The potential from transformer I43 is maintained across the terminals of resistance I15 by wires I44 and I45 each of which is connected respectively to terminal wires III and I05. The design of resistance I15 will be described later but for the present it will sufllce to say that adjustment thereof will determine the load for unit No. 2.' Any variation in potential between ,con-

- by cause the load adjusting motor to raise or lower through the contact-making device 38b and the relays associated therewith. The fixed or base load on this unit will therefore be determined by the setting on the master dial I and .while the power generated by the unit may have temporary fluctuations, the power will always be brought back to the desired'fixed load.

Any number of units similar to unit I can be added and controlled in the same manner as unit 3 is controlled with respect to unit I through its resistance I42 and corresponding devices on unit No. I. Additional units similar to unit No. 2 may also be' added and controlled in the same manner as unit 2 with respect to resistance I15. The interconnection of the controls of these units may be made in the same manner as described for unit No. 2 with respect to unit No. I, illus-.. trated diagrammatically in Fig. 8 where the" simultaneously with similar units Nos. and s a,oso,sss

" shown as curve a, Fig. 12, be secured. This rep- I resents the relation of the output on unit 2 with V 7 through master load setter I4II, there will be described iirstthe manner in which the special design, and also:;,thef relation, between the two master load settingr'esistances I42 and I"; can

be determined by the relation of the character'- 5 istic curves of unit 2 with respect to say unit It is a well established fact that for units of similar characteristics the total output of the combination must be divided equally between each unit in order to obtain the maximum com- ,acteristics it is necessary to establish curves of fuel or water consumption with respect to output. This is represented in Fig. .10 where curve d shows the approximate performance of units I and 3 as described previously. However, in the case ofunit No. 2 which has a diflerent characteristlc curve e, shown in Fig. 10, the slope of this characteristic curve is radially diflerent 85 from that shown on curve d representing the performance of units I and 2.

It is furthermore a well established fact that the most economic distribution of load between two units of dissimilar. characteristics maybe 80 determined from their characteristic curve by taking the slope of the characteristic curve at various points. For example, between is on curve d the slope would be represented by the ordinate ck: divided by 1k and on curve e by 7'1 85 divided by hi. If the slopeis determinedat each point such as m an non each curve these can be plotted'with respect to the discharge through the units shown as curve p, Fig. 11, for units I and 3 and r for unit 2. The area'represented under the respective curves is a direct proportion of the output of the respective units and from an analytical study it has been determined that the economic combination is that where the two units are operating at the points of identlc slope of their characteristic curves as illustrated in Fig. 11. I

With curves p and r the most economic combination for operating at a'totaldischarge of Q would be represented by the points s and t where point t corresponds to Q: on unit 2 and point s corresponds to Q1 on unit I. This relationbetween discharge on the two units can be converted to output on the two units and a relation respect vto the output on units I or 3 for the maximum economy of the combination of units 2 and 3 at. any given load. L A If this relation, modified if necessary for local to requirements, is established then there is determined the relation between master load setting resistance "5 and I42 so that at any setting ofdial I55 for a given total load the potential corresponding to the relation shown incurve a, Fig. 65 12, will be transmitted tothe galvanometer circuits of those units which might be connected to the master load setter and consequentlythe connected units through their control mechanism will maintain this ideal relation.

7 Economic load distribution between all units.-

.In operation, to eifect automatically the economic distribution of load betweensimllar and dissimilar units I, 2 and {when .set at a con-- stant value by'the master load setter I4Ithe moved simultaneously between certain contacts,-

some of which are'dummies as will be seen by the fact that no wires lead therefrom. It will be understood of course that this selector switch may be of any suitable type having multiple contacts. In this arrangement potential from transformers I43, ll, Ila and Ilb is applied to the combination master load setting resistances III and I15, and to unit load transmitting resistances I2, In: and l2b as hereinbefore described. To insure a constant and uniform potential at the supply terminals of each resistance there is provided "the multiple lead wire I" previously dwcribed. The multiple lead is also connected through wire III, across switch AIl, wire 202, across switch A-Ii, both of which are closed in this arrangement to make the necessary connections, and through wires "3 and 204 to terminal wireilb of resistance lib. Thus allof the terminal points of resistances I42, I15, I2, I2a, and. lib are connected to a common source of potential and also these resistances are connected to one side of the individual transformers. while the other side of these transformers is connected to In connection with the galvanometer circuits for units I and 3, potential is transmitted from contact I", wires I, across switch A2 to wire "I, across'switch A-I to wires ltl and I52,

switch II closed in position III and on through the ,galvanometer circuit including wires 21 and 22 to contact 2|. Wire III transmits potential on through wire I52a, switch 28a set in position Illa, through-wire 21a and galvanometer 23a back through wire 22a tocontact Ila or resistance Ila.

In connection with unit No. I the potential at contact III is transmitted tocontact 2 I b as previously described.

In connection with variable resistance ilb it is essential that the resistance in combination with resistance I" be arranged with scale I55 and lbv to give a balanced potential between points I16 and Ilb when the reading on scale lb corresponds exactly with the reading on scale I". Scale lb is arranged to read uniformly the output of unit 2 as measured by wattmeter'lllb.

Intermediate taps "I and "I are provided on this unit load transmitting resistance lib in order to, short-circuit any part thereof as may be desired for signalling or for other control functions where a portionof the resistance, for example, between 350 and "I, should be made constant instead of variable, and also toprovide a potential which might be transmitted to either resistance I! or Ila as might be required in connection with other functions of the control equipment. I

Frequency cnt1'oller.-By arranging a freauency sensitive bridge such as an impedance opposite sides of the bridge.

this frequency sensitive bridge. When the frement.

a,oso,sss

bridge consisting of an arrangement of condensers and non-inductiveresistances, .one pair in par- .allel and one in series, a galvanometer connected across this bridge will indicate variations in frequency above or below the normal setting as deis supplied at 306 and 301 and'condenser I is arranged in parallel with non-inductive resistl0 ance 309 and a'corresponding condenser SID is arranged in series with a non-inductive resistance III with fixed resistances ll! arranged on the Adjustable resistances 3M and iii are provided for establishing the zero of the bridge corresponding to any desired standard frequency. A galvanometer iii is excited'by the field III which in-turn is supplied with power through leads ill and 'Illthe latter coming through switch 320 from one phase of the generatingsyste'm. The alternating current supplied across terminals ill and IIS therefore acts to supply the field and the galvanometer ill, III and also the current supply 308 and 301 across 30 quency increases or decreases from normal the galvanometer will be deflected in the proper direction due to the variation in current flow be-- tween the parallel arrangement of condenser 30! and resistance 309 as compared with the current flow through condenser Sill inseries with resistance Ill. The deflection ofthis galvanometer therefore. indicates the departure from normal of the frequency of the current supply from Ill and IIS. The galvanometer will'also deflect in proportion to the departure of this frequency from normal, as the current across the terminals of the galvanometer and hence of the bridge 323 and 824, will be in proportion to the variation in frequency, provided the various elements of the circuit are calibrated and designed accordingly.

This deflection or the galvanometer ll is transmitted to a contact making device generally indicated at "I which in cooperation with galvanometer SIC is identical in construction and operation to contact making device 16 and its cooperating galvanometer 28. Corresponding elements of the two devices have the same reference number with sufllx letter I indicating the elements of device Ii]. Contacts 59! lower the output on the-connected units in response to an increase in frequency and contacts "I increase the load on the units in response to a decrease in frequency; l

The current for the contact-making device is taken from the direct current source 85 by wires III and 325 through switch 320 and wire )28 to the neutral wire 64] of the contact-making device. The two contacts 59! and Bill are connected by the common leads 321 and 328 toall 65 units in the stationby the following arrange- Switches ll. lob and Illa are adapted when in down position to substitute the control impulses made by the frequency controller 305 for the load control impulses provided by the contact-making devices 36, 38b and 38a of the individual unit load controllers. In the operation of these switches, preferably only one at a time are in down position in order to avoid inn aocosss dition whereby unit No. I can correct frequency mentor from the generating system'to which unit ing motor 36 to decrease the output of unit I. If

t q p To accomplishthis preferredoperation of a. I

' dividual switch 13, Ila and lilb they may. becombined in a single master frequency selector-switch. similar. to the operation selector switch Ill, thus eflecting the simultaneous operation of these individual switches by means of the single master switch with the contacts arranged. forexample, toconnect any one unit control circuit to thecommon leads 321 and 323 and withthe remaining units connected to their individualunit load controllers. Under certain circumstances two or more units may be simultaneouslyconnected with commonleads 321 and 323.

Type III-a Operation: Frequency control by all units or onIyoneL-JI only unit No. I isconnected to the automatic control apparatus, switches lllb and Illa are opened, switch 13 is closed in down position and the operation selector switch III is set in position III. The apparatus is then in convariations from normal as indicated by the deflection of galvanometer II! which issensitive to the frequency supply from the generating equip- No. l is connected. This frequency correction is effected by adjusting he load on unit No. l in accordance with the f uency variation. with "switch 13 in down position, contact 30f is connected to relay 33 by wires 321 and 31 to the. other side of the source of current as previously described when current is supplied from contact 33. Closure of relay" energizes raising field 93 of the load adjusting motor 33 as previously described. Closure of contact 33! causes relays II to beenergized by a current impulse transmitted through wire 323, switch 13 and wire 12 to relay 13 thereby to energize lowering field 32 of the load adjusting motor as previously described. Switch II-- by being in down position prevents any transmission-of load control impulses to the load adjusting motorfrom the contact-making device 33. Switch 13 in down position closes contact between leads 333 and 333 to short circuit the. leads to galvanometer 23 which is thereby maintained neutral and. does not oscillate back and forth. Thus it is that this controller need not be operated when unit No. l is arranged to.

maintain frequency. control. When switch 10 is in apposition, leads 333 and 333 are open and hence the galvanometer 23 is free to move in response to differences in potential between variable resistances l2 and I3 or resistance l2 and H2. l

In the frequency increases above some normal value as determined by the setting of the balanced position of the'impedance bridge as indicated by the setting of a dial 333, the galvanometer 3l3 through the contact-making device'33l closes contact 59f and relay I3 causing the load adjustthls control impulse is not suillcient to restore thefrequency to. normal, galvancmeter 313 causes additional contacts to be made with point 33! until the frequency is restored to normal. If

on the other hand'the frequency is below normal, galvanometer 3l3 will deflect in the opposite direction closing contact 30! andtransmit a controlimpulse to relay '33 to raise the output of un t No. l by means of control motor, 33 and the eby restore frequency to normal.

p The length of time that. contacts 33! or 33! are closed is, as explained with device 33. in direct proportion to the deflection of the galvanometer v ti'on of the units on type djcontrol? in whichinxm a in direct proportion to the variation of frequency. from normal. As a result the corrective-control impulses transmitted to unit No. l are in proportion to the variation of frequency'frorn normal. s It is a well established fact that variations in spqd of generating equipment supplying electrical energy for commercial service, are a funcfrequency controller 33lwith its galvanometer vlce 33! and other relay equipment to actuate fload adjusting motor 33, the variations between;

supply and demand are automatically compensated for, and hence tend to maintain ,thejfrequency at a constant value." While it '.is:necestion of the. diiferencebetween thepower demand and the power supply- Hence, by means of "the sar'y to have a variation of frequency from normal to initiate operation of these control im pulses still the control devices tend to reduce the departure offrequency-frun' normalto merely a frequency tolerance which is of greatly smaller value than would be the case if the speed of the generating equipment was controlled solely by the speed governor without the automatic equipment as described. This frequency toler-' ance is extremely small since the galvanometer is far more sensitive to small variations in frequency than itis possible to build the commercial design of turbine speed governor, and also because thecontrol device as arranged does not have the inherent speed drop from no load tofull load which must be included with aprime mover gov-- crnor. The usual permanent variationgln final speed following a load change is automatically compensated for by my improved control device by restoring the to normal and hence cor-. recting for the inherent speed change of the governqr mechanism.

It will be seen, therefore, from the arrangement and operation of thelfrequency controller'335,and

thecontrol and relay mechanisms which actuate load adjusting motor 33;..thatithisfunetion of restoring speed to .normalfisindependent of the output of unit No. I slncethe load controller 33 is disconnected from the devices acting upon loa adjusting motor 33. This same arrangement of frequency control can be applied to any additional unitsby merely.

closing one or both of switches lllb'or 10a in down position 1 whereby impulses supplied by contacts 39! or 30} will be transmitted to load adlusting motor 3311 or 33a in exactly the same manner as described with load adjusting motor. 33.

Corresponding elements in each of the units for this arrangement also have the same reference number with the sufilx letter a or b'to indicate unit 3. or 2 respectively.

With any unit, frequency control thereof is independent of the load on the unit as indicated by its respective watt-meter. ;.Hence, the output of the units is determined bythe'response of the individual speed governor to the. control impulses on its respective load adjusting motor and has no relation to the load on any other unit in the combination. It is obvious frcmflthisarrange ment as just describedthatjtheemciencypo combination will not be maintainedautornati] at a high value as is the c ewith the 015 as described previouslyl. I,

Type III-b operamn 1min control with economic unitslondldperatinozj the emciency of the combination is not sacrificed by operation on irequency control, the combination oi units can be arranged as described hereafter to actually obtain frequency control with economic distribution of load between units when operating together. Assuming the combined frequency and economic load distribution is desired with similar units 1| and 3 operating together while unit No 2 is inoperative, switch ll! remains in down position while switch Illa is placed in up position, see Figs. 1 and 8. The galvanometer 23a is then connected to be sensitive to any variation'in potential between points 2| and 2|a on units Nos. and 3 respectively, the circuit being from point 2| through wire 22, galvanometer short circuit wires 334, switch 10, wires 333, switch 23 closed in position ill, wires I52, I52a, switch 28a closed in position Illa, wires 21a, 24a, galvanometer 23a and wire 22a to point 2|a.

In this manner if the frequency departs from normal and the load is changed on unit No. l,

the increase or decrease in output causes wattmeter in to adjust resistance l2 and. vary the potential at point 2|, this variation in potential being transmitted through the circuit of galvanometer 230 as above described thereby adjusting relays 13a or 88a and hence operating load adjusting motor "a in such a manner as to maintain the output of units Nos. I and 3 identical.

It will thus be seen that as the output of unit No. l is varied in accordance with the requirements for frequency control, the output of unit No. 3 is also varied in the same manner by the control impulses relayed from unit No. to unit No. 3 .due to watt-meter Ill operating to vary resistance I2 until such time as the potential at points 2| and 2|a are equal and hence the two units have the same output.

'Fig. 8 shows a diagrammatic arrangement of this load equalizing circuit where galvanometer 23 would be short circulted by wire 333 and 334 .with-switch'1ll closed. selector switch 130- would have its individual switch A-2 open and hence point I" would be disconnected from the common lead IBI. with short circuiting switch 10a open, potential from point 2| is transmitted directly through galvanometer 23a to be balanced against the' potential at point 2|a. Deflection of galvanometer 230. as described above will cause the load to be adjusted on unit 3 until a balanced condition ex- This. same arrangement can be used with any number of similar units whereby the maximum ihfiirervice. This isthe case where all the units '"haye; the same characteristics and simply requires the galvanometer circuit of galvanometer 23d;, Flg. 8, of each additional unit to be bridged across its watt-meter operated resistance and the point 2| as above described for unit No. 3.

, jTj/pe III-c Operation (contd) Dissimilar unit controlling frequency with similar units following: Economic load distribution between all unit s.--'Itis seen from the previous discussion where similar units and 3 are operated together to control frequency, the combined load on these two units may rise or fall as is necessary to main tain normal frequency and meet the system load The main operation 22b, short circulting wires "lb and 333!) closed "In this manner and as is more clearly seen from a,oso,ssa

demand. However, units and 3 have identical characteristics. Where a unit such as unit 2 has characteristics dissimilar to the other units and itis attempted to use this dissimilarunit to control the frequency it is seen that, as increased 5 or decreased power is necessary to maintain frequency, unit No. 2 must have its power output controlled differently from units and 3 if the most economic load distribution between the three units is to be maintained during fiucl0 as in the case of controlling frequency, the

master load setter llll cannot be used to maintain the proper power division between similar and dissimilar units. Hence to obtain the most economic distribution of power with a fluctuation in the total output, watt-meter operated resistance |2b is arranged so that its resistance characteristic bears a certain relation to the angular displacement of watt-meter llb, so as to cause the potential at point 2|b tobe equal to the potential required at points 2| and 2|a corresponding to the proper output of units and 3 as fixed by the relation of curve a of Fig. 12. This relation is exactly the same as the relation between master resistances HI and I'll.

To accomplish the desired operation, switches 109, Iflil'b and lllfla are closed. switch l03"b is open, switches 23, 28b and 23a are in positions I, lllb and Illa, switches l0 and Illa are closed in up position while switch Illb is closed in down position. The operation selector switch I3. is in its position III. The circuits completed by this particular setting of the switches will be as follows: potential from point 2| is transmitted through wire 22, galvanometer 23, wire 21, switch 28 and wire I52 to ll2a which leads to and across switch 28a to wire 21a, galvanometer 23a and wire 22a to point 2|a. The potential at point 2") on resistance l2b is transmitted through wire by switch 10b, wire in, switch as, wires mo and I30, across switch A4 to wire 232, across switch A-3 to wire 203 across switch lli'b to wire 3 which is tapped into neutral lead lll.-

the isolated and simplified diagram, Fig. 13, the 55 potential transmitted from point 2") is balanced by galvanometers 23 and 23a against potentials existing at points 2| and 2|a respectively. This is shown in. Fig. 13 by' havingswitch A-2 open and switch A-3 connected to switch A-l instead of A-|2. Switch 10b is closed to short circuit galvanometer 23b and transmit the potential at point 21 directly to the common lead Ill. The galvanometers 23 and 22a through their contactmaking devices adJust the load on units and 3 until the potential at points 2| and Na respectively are balanced against the potential at 2|b.

In special cases it may be desirable, as shown in Figs. 1 and 14, to include intermediate wires 70 35| which forms the other tap wire into resistance (5 Y no. .This insures that avconstant potentialiwill bemaintained at contact iIa-so lon'ga's it enga' any part of the intermediate short-circuited portion. Figure 14 is the same as Ii'ig. 13 except for the intermediate taps on slide wire lib and the corresponding circuits leading up to the switch A-l. Beyond switch A--8 'common lead III and other portions of the circuits are identical to Fig. 13.

fluctuations in load on unit i, is obtained when any part of the short-circuited portion ofresistance lib is engaged by contact ilb at which I position a constant potential is had corresponding to the proper amount to maintain the proper relation between the loads on the units as shown by curve 14. This potential is maintained on the galvanonieter circuits of units .I and I. .Wlth a constant potential on these galvanometer circuits there is no deflection of thegalvanometers and accordingly the contact-maklng devices It and "a will be-maintained ina neutral position, and

thus not in any way actuate the load adjusting motors I. or 860.. Power on these two units thus willbe held at the desired constant value. However, if the system frequency changes; frequency ause current impulses to be r the other of relays lib or controller in! will transmitted to one jlb thereby actuating the load adJustlng motor 66b in a direction epending upon whether the change in system load or frequency is above or below normal. Upon actuation of load adjusting motor 56b watt-meter lib aisomove to thereby change the power of unit 2 as required. This causes resistance lib to be rotated without aifecting inany way the power output of units I and. i which remains, constant so long'as contact .ilb is within the range of the short-circuited constant potential portion of resistance lib.

l-lowever in accordance with curve a, Flg.'l2, it will be seen that from point to on, any increase p in load on the dissimilar unit No. 2 shouldbe accompanied by an increase in load on units I and 3. This is accomplished due to the fact that the point at which wire "I is tapped into resistance Iib represents .point w in curve u. whereby it will be seen that an increase in power output on unit No. i, to theextent that contact ilb passes beyond tappe'd wire "I, an increase in potential will thereafter be impressed upon contact 2 lb and accordingly upon the galvanometer circuits of units I and i whlchwill then-increase their load in the proper proportion to this increase on unit No. 2. Thus the best combinedemciency for the three units will be had while still allowing fluctuations in the total output to maintain frequency or to meet the power demand on the system..

,The same thing will hold true if the load on unit 2 is decreased below the arbitrarily. fixed point except that point iI will move past point itliin the direction of I 96b, thus decreasing potential on common lead II and hence decrease the output on units I and 3. This arbitrary point is igixed from the point of view of practical considerations to reduce load on units I and I along line 03 instead of abruptly on the line 01 The amount of output on unit i represented by the displacement between points so and u is lined ials-j by switch It across wires iii and I" while galvanometer its is connected between .flected accordingly and acts to adjust motor "a at avalue eqpalto a small ymmrtionoithgoutput of unitri anddoecnot seriously impalrtlief f combined economy. When this point is reached it indicates that the surplus units should be shut down sothattheload canbe Type III-d Operation :(cont'd) Frequency control by unitslvos. 1 and 2 combined, or units 1; 201-3 olmse-Ifforaflreasonlessthanthiee units are required. a schedule of operationto be lowed by the operator will lndicatethe proper unit to'be shut down-in order to maintain the best combined efllciency for the remaining units.

For example, if this should be unit No. i, switch use would be opened, cuttlngoll the control from this unit. The remaining two units l and i, would then operate in the same manner as the combination of more than two units, because potential from. point ilb would be transmitted 1 through galvanometer ii to point iI and the load on unit I would increase or decrease in accordance with the variation of thispotential as determined by the output of unit i through the watt-meter control of resistance lib with its short-circuited portion. If unit I were no, longer required for service, switch I" would be opened and the cire cult between points ilb and iI would be broken. whereby unit 2 would then be: operating along on frequency controland also following the requirements for frequency correction. 3 If however, unit 2 is no longer required for service then the trequencycontroi could be transferred toeither units I or 8. Assuming. that unit I is required, switch lbi will be closed, switch I! closedin down position and switch as closed, whereby unit I will have its output automatically adjusted in accordance with the deflection of gal vanometer iii aspreviously described..

1 If unit 3 is required for service in addition to unit I. switch lIiOa isclosed and switch 10a is closed in up position. The primary frequency corrective impulses are still transmitted through switch III in the down position to unit I from wire lil or I28. 'Galvanometer i3 is short-cirpoints iI and ila'to variable resistances Ii and lid respectively so that as the load increases or decreases on unit I galvanometer 23a is dein such a manner as. to. maintain anooutput on unit 3 equal to the output on unit I which is the requirement for maximum economy of operation for the combination since it is assumed that units I and i have identical characteristics.

The same scheme of operation can be reversed. and the primary impulses i'orirequency correction applied to unit i by closing switch Illa in down position and closing switch "in up position. The frequency corrective impulses initiated by galvanometer ili arethen transmitted to load adjusting motor "a from'wire Ii'l or iii. Galvanometer its is then short circuited by switch "a across wires 333a and 834a while galvanometer ii is placed between points il 7 and ill: so that load adjusting motor 88 is operated to equalize the load between units 3 end I.

In connection with the function of variable resistance lib, it .will be desirable in certain cases to utilize two resistances lib and lib instead or one; The first of which '(Iib') will be con- .nected in combination with resistance ill of master load setter III with Type IV, operation (station base load) and the other for use in connections;

carrled tor economi s caliy on fewer units.

' inn the distribution of load between units I and i-when unit2 is controlling frequency on type III operation. The operation selector switch I90, would connect point I16 withpoint 2lb' on vari-' able resistors I2b'- for type-IV operation. In

the case of type III operation, the operation selector switch would connect common lead Ill, and hence galvanometersfl and 23a, to point '2Ib" on resistance I2b".

- .these units. The necessary additional unit con:

trol equipment, designated by sum: letter d in Fig. 11, would be connected to common leads Iii,

I88, Figs. 1, B, 13 and 14.

In connection with additional units having characteristics different from those of either units I, 2 or 3. special supplementary variable resistances (I2e) Fig. 14 corresponding to resist- 'o ances l2, I2a, or I2b can readily be provided on one or more units so that any particular unit can determine the loading on any other unit for the requirements of maximum combined efliciency. This resistance He will transmit to some additional unit, for example unit I, a potential from point 2Ie which, through its galvanometer 239 will cause the output to be adjusted until the potential at Zia equals potential at 2Ie and the additional unit is carrying the desired amount of load. The relation and arrangement of slide wires l2e with respect to the given units to which they are applied will be determined by economic studies similar to those described for Figs. 10, 11 and 12. It is understood of course that where-certain units are particularly adapted by their characteristics to operate at fluctuating loads while other units should maintain constant load for purposes of .economy, that the primary control of frequency should be placed on the units particularly adapted for variable load operatlon' when that unit or units are in service in preference to placingthe primary control on a unit which from its characteristics is not adapted to having the primary control of frequency placed thereon when units more adapted to this type of service are in operation.

Type I operaticm.The purpose of this operation is to allow only a fixed output from units I and 3 by use of the master'load setter and to control frequency with unit 2 which, aside from a protective circuit, is operated independently of the other units. The controls are arranged in such a manner that frequency controller 305 transmits frequency corrective impulses to unit 2 from either wires 321 or 328 through switch 1Ilb closed in down position. I v

Operation selector switch I is set in position I whereby the controls of units l and 3 are connected through the master load setter "II in such a manner that the output of units I and 3, or

either of these units separately, are set by the position of the dial I". The potential at point 2| is transmitted through wire 22 to galvanometef' 23 and then through wires II, 21, I52 and III to and across switch A-I .to wires "0, across switch A-2 to wire I to point I" on the master resistance I42. A similar circuit is also completed through galvanometer 23a between points 2 la and I", the circuit being from point 2Ia through wires 22a, 24a, 21a and I52a which is tapped'into wire Iii of the circuit just described to connect 5 with point I". To complete these circuits, either or both of switches 28 and 28a are closed in position Ill and Illa depending upon if only one or bothunits I and 3 are-in service. Switches I09 and "Na are closed and'switches III and Ilia are 10 I 23b is short-circuited and frequency control imiii! pulses transmitted to its load adjusting motor from either of wires 321 or 328.

Type II operation: Frequency control by unit No. 2, with base load and frequency standby on units 1 and 3.If the arrangementdescribed as 25 Type I operation is applied to plants where the varlationin demand required for frequency control may exceed the capacity of a single unit, for example, unit 2, a method of inter-connected operation is arranged which will give the equivalent of type I operation and still meet the variation in demand. 1 v

To accomplish this, unit 2 is operated normally to maintain constant frequency and units I and I are maintained to .give a iixed combined load, 35

' or base load, as set by the master load setter llll.

A cross-connection defines a zone of normal operation in which the power capacity of unit 2 may fluctuate to maintain frequency during":which time units I and I are maintained at a fixed combined load. Also, when unit 2 exceeds the limits at either end of this normal zone, it will operate in an auxiliary zone which relays potential to the controls of units I and I in such a manner as to increase or decrease the output thereof to assist unit 2 in maintaining frequency. This scheme is therefor the equivalent of unit 2 maintaining frequency while units I and loperate on base load with frequency standby connections which will cause these units to step in and assist unit 2 in controlling frequency if the power demand for frequency control exceeds or falls below the capacity of unit 2.

To effect this arrangement, see Figs. 1, 1a, and 14, operation selector switch I" is set in position 55 II and other switches are set in the same position as described when switch ISO is set in position I. Hence for normal operation unit 2 receives control impulses from frequency controller ll! with switch 10b set in down position. Units 00 I and 3 are operated at a desired load as set on dial- IUI of master load setter IlII all as described for type I operation. In addition the constant potential segment of resistance I2b is short-circuited by wire 350, across switch A-I 55 to wire 362 and switch A-| to wire "I. With the power of units I and 3 determined by-the setting of dial I 53 on master load setter Ill any variation in the output of units I and I from the potential as determined by point Ill 70 will be corrected by galvanometers 23 and 23a respectively through their proper contact-making devices. However, so long as the power of unit 2 fluctuates between such limits that point 2Ib moves between the resistance taps of wires-ll 

